Hydrocarbon dealkylation process



NOV. 29, 1966 J HAMMOND ET AL 3,288,876

HYDROCARBON DEALKYLATION PROCESS Filed June 27, 1963 OFF GAS f RECYCLEGAS INVENTORS JAMES 0. HAMMOND BY JOHN w. PAYNE LEO A.CASTLER ATTORNEYUnited States Patent York Filed June 27, 1963, Ser. No. 291,208 17Claims. (Cl. 260-672) The present invention relates to the dealkylationof feed stocks containing alkylaromatic hydrocarbons, especially thethermal dealkylation of such hydrocarbons in the presence of hydrogen.It is particularly concerned with the production of benzene by thermalhydrodealkylation of alkylbenzenes.

Alkylaromatic hydrocarbons have been subjected to hydrodealkylation inthe presence of catalysts and also in non-catalytic thermal reactions.In one series of comparative tests, the thermal method has been found tohave a number of significant advantages over the catalytic treatment.Among these benefits are producing higher yields of benzene ornaphthalene, less cracking of aromatic rings and lower dry gas yields;consuming less hydrogen at any given conversion level, reactin g atfaster rates and showing less proclivity to lay down coke in theapparatus.

A :great deal has been written on the thermal hydrodealkylation ofalkylaromatic hydrocarbons but little or no recognition has been givento the related problem of metal dusting which often occurs in suchreactions. This is a form of corrosion so rapid and destructive as to betermed catastrophic corrosion. Apparently a carburization of the metalor alloy takes place that causes grains of metal or a metal carbide todrop out of the walls of processing equipment, as analyses haveindicated both types of substances along with carbon to be present inthe dust found in the bottom of a thermal hydrodealkylation reactor.However, the phenomenon is not yet fully understood.

This corrosive action is so fast that it has been observed to penetrate18-8 stainless steel tubing within a matter of four or five days attemperatures of the order of 1320 F. in another hydrocarbon conversionprocess. Even some higher chromium-nickel alloy steels are seriouslycorroded in a short time. The common practice of constructing pipes andvessels with walls of extra thickness to provide corrosion allowancesdoes not appear to be a feasible countermeasure against such rapidattack.

Metal dusting occurs particularly when a metal surface is exposed to amixture of hydrogen and a lower hydrocarbon, such as methane, etc., attemperatures of the order of about 1275 or 1300 F. and higher. It isalso possible that this'destructive reaction occurs at lowertemperatures over a long period of time. An increase in the proportionof lower hydrocarbon relative to hydrogen has been observed to increasethe degree of corrosive attack. The problem is particularly acute withthe dealkylation of a straight or n n-blended alkylaromatic hydrocarbonstock such as nitration igrade toluene in the presence of ahydrogen-methane mixture.

An object of the invention is to provide an improved process for thethermal hydrodealkylation of alkylaromatic hydrocarbons.

Another object of the invention is to provide an improved thermalhydrodealkylation process for the conversion of alkylaromatichydrocarbons wherein little or no metal dusting occurs throughout thesystem.

A further object of the invention is to provide for the thermaldealkylation in the presence of hydrogen of an :alkyl benzene in whichsubstantially no corrosion is ,encountered in the processing apparatus.

3,288,876 Patented Nov. 29, 1966 Further objects and advantages of theinvention will be apparent to those skilled in the art uponconsideration of the detailed disclosure hereinafter.

The present invention is concerned with a combination of processingconditions in a dealkylation process comprising indirectly preheatinghydrogen and a normally liquid alkylaromatic hydrocarbon feed stock in aratio of at least 4000 standard cubic feet of hydrogen per barrel ofsaid feedstock underconditions wherein the maximum temperature of heattransfer surfaces in the preheating zone in contact with said charge ismaintained at not more than about 65 F. (preferably not more than about50) above the temperature of the proximate portion of said charged,introducing said preheated charge at a temperature between about 1100and 1175 F. into a dealkylation zone, and dealkylating said preheatedcharge at average reaction temperatures between about 1200 and 1275 F.for a period suflicient to effect the conversion of at least 65% byvolume of the alkylaromatic content of said feed, based on disappearanceof alkylaromatic compounds.

Another important aspect of the invention relates to producingsubstantial internal circulation in the dalkylation zone to quicklyboost the temperature of a charge through a substantial range to atemperature high enough to induce an effective dealkylation reactionrate and also to prevent excessive reaction temperature. This may beaccomplished by injecting the charge into a reactor as a high velocityjet at a nozzle velocity between about and 850 feet per second.

Narrower aspects of the invention relate to quenching the reactionproducts with a vaporiza'ble liquid, a comparatively lon g reaction timebetween about 30 and seconds, introducing normally gaseous hydrocarbonswith the charge, charging relatively low proportions of hydrogen topermit a relatively low degree of preheat and a large temperatureincrease upon a mixture with the hot circulating reaction mixture. Inthe case of toluene, the hydrogen charge is desirably between about 3.5and 6 mols of hydrogen per mol of toluene. The charge ga-s alsodesirably contains between about 0.2 and 1.2 mols of normally gaseoushydrocarbons per mol of hydrogen. The volumetric ratio of recirculatingreaction mixture to fresh change may be between about 2:1 and 15:1,respectively, and preferably is between about 4:1 and 10: 1.

The instant process is designed to avoid the problems occasioned bymetal dusting in thermal hydrodealkylation under conventionalconditions. Especial attention is given to the matter of avoidingtemperatures in the metal dustinig range, that is temperatures at whichthe metal dusting or carburization reaction proceeds at a significantrate, while maintaining satisfactory dealkylation rates in equipment ofreasonable size. The lower temperatures, an important feature of thepresent invention, not only eliminates or at least minimizes the metaldusting problem but also enable one to use construction materials withthinner walls or lower alloys or both in view of the well known factthat all metallic construction materials lose a great deal of theirnormal strength at high temperatures. This emphasizes the need forrunning such reactions at the lowest possible temperatures sinceconsiderable pressures are desirable in thermal hydrodealkylationreactions.

Mention is made herein of a certain temperature dif-' ferential beingheld within a range of 65 F., and preferably within 50, in thepreheating furnace. This refers to the difference in temperature between(1) the maximum temperature at any point on :a heat transfer surface incontact with the charge (usually the inner surface of an externallyfired tube or coil) of all of the heat transfer elements in the furnaceand (2) the proximate portion of the ch argethat is the part of thecharge which is in the same location, region or zone as the point on theinternal surface where the aforesaid maximum temperature is attained.Generally, this point is located near the charge outlet of thepreheating furnace. It should be noted that the stated temperaturedifferential applies only in the region of the maximum tube temperaturebecause greater temperature differentials are permissible at otherlocations, as for instance, near the charge inlet of the heater. It hasno application to any preliminary heat exchangers, etc. for the charge,which are located upstream of the preheating furnace, as their highestsurface temperatures are below the surface tempenatures to which thecharge is exposed in the preheating furnace.

The dealylation reaction may be carried out in several different kindsof reactors. The preferred type provides rapid internal recirculation ofthe reaction mixture with thorough mixing of the charge therewith in themanner described and claimed in the concurrently filed application, Ser.No. 291,100 of John W. Payne et al. entitled Hydrodealkylation ofAlkylaromatic Hydrocarbons. Good control of the relatively low reactiontemperatures and rapid heating of the charge entering the reactor aboveits low degree of preheat are among the signficant features of theinvention, and internal recirculation is a good means for obtainingthem. A suitable internal recycle reactor is illustrated in theaccompanying drawing.

Another suitable reactor is the single pass flow reversal type describedin detail and claimed in the concurrently filed application, Ser. No.291,077 of Vernon O. Bowles entitled Apparatus and Method for HighTemperature Reactions. This reactor comprises two concentric tubes withthe inner tube open at the bottom to provide an annular zonecommunicating with the inner cylindrical zone at the bottom only. Thecharge is heated in the upper portion of the annular space by acombination of external firing and indirect heat exchange with thereaction products, then it is reacted principally in the lower annularzone and lower part of the central passage. The lower annular zone isdesirably in indirect heat exchange with a second and separate externalheat exchange medium. Fin-ally the reaction products in the uppercentral passage transfer a sizable amount of their heat content to theincoming charge in the surrounding annular zone.

While the above two reactors will generally facilitate better control ofthe highly exothermic hydrodealkylation reactions, a plug flow reactor(i.e., a single pass straight flow reactor) may be used if someprovision for removing sufiicient heat to avoid excessively highreaction temperatures. In order to keep such a reactor within areasonable size it will also probably be necessary to heat the firstsection of the reactor sufficiently to bring incoming charge quickly toa commercially feasible re: action rate.

With any of the reactors mentioned, the level of the reactiontemperatures may be raised or lowered by in creasing or decreasing thecharge inlet temperature by suitable operation of the preheat furnace.Usually the inlet temperature is at least 70 F. below the averagereaction temperature. V

The combination of the present invention also includes careful controlof the hydrogen charge. The use of a relatively low quantity of excesshydrogen and accom panying and inert diluents therewith permits theexothermic heat of reaction to more quickly heat the entire charge tothe selected reaction temperature; however, the inlet ratio of hydrogento alkylaromatic hydrocarbons should not be allowed to drop to the pointwhere the deposition of carbon in the reactor occurs. The hydrogen ratemay be maintained in most instances between about 4,000 and 8,000standard cubic feet per barrel of liquid hydrocarbon feed referring to42 gallon barrels and cubic feet measured at 60 F. and 29.92 inches ofmercury pressure (hereinafter abbreviated as s.c.f./b.). For toluene ormonomethylnaphthalene undiluted with other hydrocarbons, the preferredrange is between about 3.5 and 6 mols of hydrogen per mol of toluene,whichis equivalent to between about 4,500 and 7,500 s.c.f./b. oftoluene. Polyalkylated benzenes or naphthalenes combine with morehydrogen in the dealkylation reaction than the monoalkyl-a-romaticcompounds. Accordingly, a greater hydrogen charge is desirable whenthese compounds are present in quantity and the same is true of normallyliquid nonaromatic hydrocarbons which tend to crack underhydrodealkylation conditions and then consume relatively large amountsof hydrogen in hydrogenating the cracked fragments. For the dealkylationof high boiling alkylnaphthalene feedstocks with a substantial contentof normally liquid nonarmomatic hydroc-arbons that crack readily underhydrodea-lkylation conditions, a hydrogen charge rate between about8,400 and 21,000 s.c.f./b is preferred; see the concurrently filedapplication Ser. No. 290,942 of Edward J. Moll, Jr. entitled ThermalHydrodealkylation of Naphthalene Precursors.

The least expensive source of hydrogen usually available inpetrochemical plants are the 0H gases of catalytic naphtha reformingoperations and these always contain substantial amounts of lowerhydrocarbons along with the hydrogen. Within limits, this is desirablesince it has been found that such gases tend to provide a somewhathigher dealkylation converson than undiluted hydrogen. Moreover, methaneinhibits coke formation under the reaction conditions herein. Thus, itis desirable to have some normally gaseous hydrocarbons in the charge;but such inert materials and excess hydrogen function as a heat sink orreservoir in the reactor thereby requiring a higher degree of preheatingof the charge, so excessive quantities of these inert diluents are bestavoided here. It is recommended that the gaseous charge contain betweenabout 0.2 and 1.2 mols of such hydrocar-' bons per mol of hydrogen.

The total pressure in the reactor may be maintained between about 250and 800 pounds per square inch gage pressure (hereinafter abbreviated asp.s.i.g.). It appears that ring cracking occurs to an undesirable extentat pressures lower and higher than that range, and coking problems areencountered at pressures less than about.

250 p.s.i.g. It is further recommended that the inlet hydrogen partialpressure be maintained between about in close proximity to the reactionspace, for example, in

a small compartment within the shell of the reactor separate from thereaction space and located near the outlet. For a better understandingof the nature and objects of the present invention, reference should behad to the accompanying drawing which is a flow sheet or schematicdiagram with many details omitted which are well known to those skilledin the art. In addition, the tubular example hereinafter sets forth theflow rates and composition of all of the significant streams ofmaterials in the system identified by the same reference numerals as inthe drawing. Nitration grade toluene is introduced at a constant rate inconduit 4 as the material to be dealkylated. A circulating gascomprising recycled, normally gaseous products of the reaction and alsohydrogen-rich make-up gas are added from line 6 to the toluene. The twostreams are commingled in pipe 8 at a temperature of F. and a pressureof 660 ps.i.g. I t

The mixture of liquid gases is now heated by the interchange of heatwith the reaction effiuent in two steps. The charge is divided betweenline 10 leading to the heat exchanger 12 in which all liquid componentsin that charge stream are vaporized and the by-pass line 14. A portionof the charge leaves the exchanger 12 at a temperature of 540 F. in line16 which leads to the 3-way valve 18. This valve may be adjustedmanually to by-pass enough of the charge to line 14 around the firstheat exchanger 12 in order to maintain a temperature between 375 and 480F. in the inlet line 20 to second heat exchanger 22. It is consideredmost desirable to have the charge in line 20 at a temperatureapproaching the lowest temperature at which the entire charge is safelymaintained in'the vapor state under the prevailing pressure of 645p.s.i.g., that is about 375 F. With the charge completely vaporized,there is no danger of slugs of liquid creating excessive thermal shockby sudden chilling of the heat transfer surfaces in the secondexchanger. The heated eflluent from exchanger 22 at a temperature of830-910 F. depending on the cleanliness of the tubes therein and apressure of 625 p.s.i.g. now passes through the line 24 to thepreheating furnace 26 wherein the temperature is further boosted to 1125F. while the maximum temperature of the internal surface of theexternally fired heating tubes near the charge outlet is maintained at1175" F. or somewhat lower by regulating the burners in that part of thefurnace.

This furnace plays an important part in the present invention as theheat fluxes therein are carefully controlled. In the conventionalpreheating furnaces used for heating hydrocarbon streams to hightemperatures of the order involved here, it is common to havetemperature dilferentials between the maximum metal temperature of aninternal tube surface and the proximate portion of the charge in therange of 80 to 110 F. or more. However, by employing a heater designedfor low heat flux rates or low ratios of maximum to average fluxdensities or both, it is possible to hold said temperature differentialdown to a 50 F. spread. Such furnaces attain these results by variousdesign factors, especially those involving the number, size andarrangement of both heating tubes and burners.

One heater suitable for the purpose is a multicellular box type verticaltube heater which incorporates two independent firing zones tofacilitate the control of any desired heat distribution. The cold endzone may have a double row of tubes arranged on a staggered pitch, but asingle row of tubes spaced at least two nominal diameters apart isrecommended for the hot end zone. Firing from the hearth on both sidesof the double and the single rows of tubes from burners arranged closeto and directionally angled towards the walls creates in effect acompletely radiant vertical heating plane. The article An ImprovedPyrolysis Furnace by K. R. Wagner and S. A. Lee in The Petroleum Times(England) issue of December 14, 1962, on pages 740-741 further describesfurnaces suitable for the present process.

The degree of preheating employed with the charge is controlled by thetemperature controller 28 which senses the temperature close to thepreheat furnace outlet of the stream passing through a short transferline 29 on its way to the reactor 30 and automatically adjusts or resetsthe pressure controller 31 which regulates the automatic valve 32 todecrease or increase the supply of fuel gas flowing through pipe 33 tothe furnace. When the charge reaches about 1100 R, an exothermicreaction commences therein, therefore a temperature rise of few degreesoccurs while the charge is in transit between the furnace and thereactor.

The charge containing hydrogen in a low ratio of 4 mols per mol oftoluene feed is injected at a temperature of 1130 F. and pressure of 605p.s.i.g. through the nozzle 34 into a venturi tube or cylindricalpartition 36 longitudinally aligned with the central axis of thecylindrical reactor. The pressure in the reactor is 575 p.s.i.g. and the30 p.s.i. pressure drop through the nozzle produces a high velocity jetwhich maintains the contents of the reactor in relatively rapidrecirculating flow down the reactor venturi tube 36 and up through theannular space 38 between the venturi and the insulated wall of thereactor. The jet issues from nozzle 34 at a velocity of 500 feet persecond and the velocity of the entire mixture in the throat of theventuri is 58 feet per second. The circulation induced by the kineticenergy of the injected stream is sufficient to produce the circulationof about 7.5 parts by volume of reaction mixture per part of freshcharge injected. The average residence time in the reaction zone is 68seconds, so it is apparent that most of the gaseous material makesnumerous circuits of the continuous reaction channel.

The resulting thorough mixing in combination with the relatively smallquantity of excess hydrogen and normally gaseous hydrocarbons that playno direct part in the present reaction enable the relatively lowtemperature charge to be boosted almost instantaneously about F. intemperature to a reaction temperature of 1230 F. This is due to thelarge quantity of sensible heat avail-able in the large mass ofrecirculating reaction mixture in this highly exothermic reaction. Thehigh circulation rate also keeps the temperature throughout the reactorremarkably constant, within a range of plus and minus 10 F. of theaverage reaction temperature. Thus the entire reaction space is atsubstantially the same temperature. By restricting the diluents, that isexcess hydrogen and other normally gaseous components, in the charge toa relatively small amount; the exothermic heat of reaction raises thechange through a considerably higher temperature spread than usual, andthis effect is intensified by the high internal circulation rate withinthe reaction zone in which large quantities of hot reaction products ofhigh heat content are almost immediately mixed with the charge at thepoint of entry into the reactor. The overall effect is a large andeasily controlled rise in the temperature of the incoming chargeimmediately upon its introduction. This, of course, means that thedegree of preheating can be held lower to minimize any possibility ofmetal dusting occurring in the furnace tubes and transfer line as wellto minimize the loss in strength of construction materialsat hightemperatures.

The interior of the reactor 30 is lined with a refractory insulationboth to conserve heat and also to keep the hot reactants out of contactwith the metal shell of the reactor. This insulation not only permits areact-or shell with a thinner metal wall to be used but also obviatesthe need for a high heat resistant stainless steel. Thus, the reactormay be constructed of a low alloy steel containing small percentages ofchromium and molybdenum except for the exposed metal of nozzle 34,venturi 36 and the quench box 40 wherein the reaction effluent isquenched with a vaporizable liquid, namely a portion of condensedproducts of this reaction admitted via conduit 42. The quenchingoperation reduces the effiuent from a temperature of 1230 to 975 F.

The resulting quenched but stil gaseous products mixed with thevaporized quench fluid leave through line 44 which carries them to theheat exchanger 22 wherein they are cooled to a temperature of 630 F. andthen transferred via pipe 46 to the low temperature heat exchanger 12 inwhich their temperature is further reduced to 410 F. Conduit 48 carriesthis stream to an air cooler 50 where the stream is brought down to atemperature of 200 F. prior to being transported in pipe S2 to thewater-cooled cooler 54 in which the temperature is lowered to 100 F. Thecrude reaction products are delivered via line 56 to the high pressureseparator 58 at a temperature of 100 F. and pressure of 525 p.s.i.g.

The liquid phase condensed by the cooling separates in the separator andis drawn off under the regulation of a liquid level controller (notshown) in the bottom line 60. This bottoms stream is divided between thetwo valved conduits 62 and 64. The former carries the product liquidwhich is made up predominantly of benzene and toluene in a 3:1approximate molar ratio to a stabilizing tower (not shown) wherein thesmall weight of dissolved normally gaseous hydrocarbons is boiled ed.The resulting stabilized liquid may then be employed as a mixed solventor separated by fractional distillation into benzene high boilingaromatic hydrocarbons or gas oils, may be employed for quenching; butthe products of the instant reaction are generally preferred for thisoperation and moreover are readily available.

and toluene as is more likely. If desired, the quenching step may beomitted entirely A major portion, that is more than half, of the bottomsand all of the separator liquid in line 60 diverted into the in line 60may be recycled at substantially ambient product line 62. This procedurewould subject the reactor temperatures through conduit 64, pump 66 andpipe 42 effluent line 44 to some risk of metal dusting and expose to thequench box 40 in the bottom of the reactor 32. the second heat exchanger22 to considerably higher The flow of quench liquid is desirablygoverned by the 10 temperatures, but it would conserve the heat lost inflow controller 68 with an associated automatic valve 70 quenching. Thedealkylation temperature selected and in line 42 under the regulation ofthe temperature conthe metal dusting tendencies of the reaction mixtureare troller 72 which has a temperature sensing element pro largelydeterminative as to whether or not a quench liquid jecting into thereactor bottoms line 44. should be employed.

The gaseous phase leaves separator 58 in pipe 74 and While the instantprocess has been illustrated in full is also split between the valvedlines 76 and 78. Line 76 details for a better understandin 0f thePrinciples 0f takes off the lay-product gas for use as a fuel gas or asa this invention, it will be apparent to those skilled in the source ofhydrogen. For the latter purpose, it may be art that the invention is ofbroader scope and may be desirable to purify the by-product and alsoperhaps practicedin numerous embodiments with many variations. toincrease the hydrogen content by the removal of a Accordingly, thepresent invention is not to be regarded substantial amount of thehydrocarbon gases therein. as restricted to the specific detailsdisclosed herein except A far larger proportion of the separator gas isrecycled s hey may be included in the appended claims.' to the processthrough line 78, compressor 80 and pipe 82 We claim: and 6. In conduit6, it is joined by a makeup hydrogen- 1. A process for the dealkylationof an alkylaromatic rich gas of about 90% purity introduced from supplyhydrocarbon which comprises indirectly preheating a line 84 at apressure of 660 p.s.i.g. The quantity of Charge Comprising y g and anormally liquid alkyl make-up gas must be suflici nt to replace t onlyth aromatic hydrocarbon feed stock in a ratio of at least hydrogenamounting to 940 s.c.f./ b. of liquid feed, which 4000 -ff hy rogen perbarrel f said feed stock in a is consumed in the process but also 800s.c.f./b. of hydropr hea ing zone wherein the maximum temperature of geni th f l gas hi h i being t k 5 ti n heat transfer surfaces in contactwith said charge is mainas a lay-product in line 76, In speaking ofhydrogen tained at not more than about 65 F. above the temperaherein,reference is being made to the actual hydrogen tllfe 0f the PYOXiThatePortion of the charge, ihtfodudhg content of the gaseous mixtures andnot to the total mixed Said preheated Charge at temperature betweenabout 1100 gas. The hydrogen-rich streams generally available at and1175 E into a dealkylation Zone and dealkylatifig low cost in a refinerytypically ont i f m t 90 35 said preheated charge therein attemperatures above about hydrogen :by volume and it is seldom if evercommercially 1200 and not Exceeding about 1275 F. for a Period offeasible to use pure hydrogen. time sufiicient to efiect the conversionof at least 65% of EXAMPLE Pound mols per hour Pipe No 4 29 44 a0 64 7476 78 84 6 52 Stream Toluene Reactor Reaction Quenched Sepa- QuenchSepa- Otr Cycle Fresh Total Liquid Fee Charge Products Reactor raterLiquid rator Gas Gas Gas Charge Prod.

Effluent Liquid Vapor Gas 976.0 794.0 795.0 2.2 1.0 792.8 154 6 1.2940.6 1,132.6 1,141.9 20.0 9.3 1,121.9 218.9 10.7 15.5 21.0 22.5 3.3 1.519.2 3.7 1.8 0.8 1.2 1.4 0.4 0.2 1.0 0.2 0.2 1.8 18.8 192. 6 341. 0 319.9 14s. 4 21. 1 4. 1 171. 5 Toluene 241.3 243.5 62.5 114.2 111.5 51.7 2.70.5 59.3 Other Aromatics 0.9 0.9 2.3 4.4 4.4 2.1 2.3

Total 244.0 2,196.1 2, 205.2 2, 420.4 461.7 214.2 1,958.1 382.0 247.5

The above example represents a material balance in the alkylaromatichydrocarbon content of said feed stock. which 1764 barrels per day ofnitration grade toluene is 2. A process according to claim 1 in whichsaid reacdealkylated with a total hydrogen charge of 5040 s.c.f./ b.tion time is between about 30 and 120 seconds. to achievfi Conversion of75% by Volume based 011 3. A process according to claim 1 in which saidcharge toluene disappearance during a residence line of 68 containsnormally gaseous hydrocarbons Secimds- The vohllhe of entering the 4. Aprocess according to claim 1 in which said charge afnouflts to 1128 cub:P f Fmnute under the contains between about 0.2 and 1.2 mols of normallygastrons 1n the reactor, and this is 1n ected through a suitably eonshydrocarbons per mol of hydrogen.

sized nozzle at the aforesaid nozzle veloclty of 500 feet A processaccording to claim 1 the dealkylafion Per Second to Set up an InternalrFmrciilanon rate of of toluene in which from 3.5 to 6 mols of hydrogenis about 7.5 parts per volume of reaction mixture per part bar ed er molof toluene of freshly injected charge. Neither metal dusting nor 6 p 1 hh the deposition of any appreciable amount of coke are process'accor mgto calm 1 mw 1C Sal c f observed in the operation contalns between about4000 and 7500 standard cubic Alternatively, an extraneous quenchingfluid may be feet of hydrogen Per baxtml'of l employed in the quenchbox. This material should be A Proces? accordmg to 9 m fh l vaporizablebut substantially inert to the reaction products heatmg )Peratmn takesPlace lmmedlately Pflor to Intro under the reaction conditions and itpreferably should dhchlg Said preheated Chafge into Said dealkylatiollZonebe readily separable from the reaction products by distil- A Processaccording to Claim 1 in which the P lation; thus other streams boilingabove 275'" P. such as ucts of said reaction are quenched to atemperature below about 1000 F. in close proximity to said dealkylationzone by admixture with a vaporizable liquid.

9. A process according to claim 8 in which said quench liquid containsnormally liquid hydrocarbons.

10. A process according to claim 8 in which said quench liquid containscondensed normally liquid products of said reaction.

11. A continuous dealkylation process which comprises indirectlypreheating an alkylaromatic hydrocarbon and hydrogen in a furnace soconstructed and arranged that the maximum temperature of heat transfersurfaces in contact with said charge is maintained within about 65 F.above the temperature of the proximate portion of said charge,introducing said preheated charge with a content of at least about 4000s.c.f. of hydrogen per barrel of normally liquid hydrocarbon feed stockat a temperature between about 1100 and 1175 F. into a dealkylation zonewherein a reaction mixture is recirculating through a continuoussubstantially unobstructed channel whereby said reaction mixture iscontinually mixing with fresh preheated charge, and reacting said chargein said channel at temperatures above about 1200 and not exceeding about1275 F. for a period of time sufiicient to effect the conversion of atleast about 65 of said alkylaromatic hydrocarbon.

12. A process according to claim 11 in which the volumetric ratios ofrecirculating reaction mixture to charge are between about 22-1 and15:1.

13. A continuous process for the dealkylation of a normally liquidhydrocarbon feed stock rich in alkylaromatic hydrocarbons whichcomprises indirectly preheating a charge comprising hydrogen and saidfeed stock in proportions of at least about 4000 s.c.f. of hydrogen perbarrel of said feed stock under conditions wherein the maximumtemperature of heat transfer surfaces in the preheating zone in contactwith said charge is maintained at a temperature Within about 65 of thetemperature attained by the proximate portion of the charge, injectingsaid preheated charge at a temperature between about 1100 and 1175 F. asa high velocity jet into a dealkylation zone wherein the reactionmixture is circulating through a continuous confined path substantiallyfree of obstructions whereby said reaction mixture is continuouslymixing with said injected charge, reacting said charge in said path attemperatures above about 1200 and not exceeding about 1275 F. for aperiod of time su-flicient to effect the conversion of at least about ofthe alkylaromatic hydrocarbon content of said feed stock andcontinuously withdrawing a stream of said reaction mixture as theproduct of the process.

14. A process according to claim 13 in which said charge is injectedinto said dealkylation zone at a nozzle velocity between about and 850feet per second.

15. A process according to claim 13 in which said charge containsnormally gaseous hydrocarbons, hydrogen and toluene in proportionsbetween about 0.2 and 1.2 mols of normally gaseous hydrocarbons per molof hydrogen and between 3.5 and 6.0 mols of hydrogen per mol of toluene,said charge is injected into said dealkylation zone at a nozzle velocitybetween about 100 and 850 feet per second thereby recirculating betweenabout 2 and 15 volumes of said reaction mixture per volume of saidinjected charge, and maintaining said reaction mixture at a pressurebetween 250 and 800 p.s.i.g. for an average residence time between about30 and seconds.

16. A process according to claim 1 in which said preheated charge isinjected into a confined dealkylation zone as a high velocity jet ofgaseous material at a sufiicient initial velocity to produce rapid andthorough mixing of the material in said dealkylation zone.

17. A process according to claim 1 in which said preheated charge isinjected in gaseous form into a confined dealkylation zone at a nozzlevelocity of at least 100 feet per second.

References Cited by the Examiner UNITED STATES PATENTS 3,149,176 9/1964Glazier et al 260672 3,182,094 5/ 1965 Glazier et a1. 260672 3,201,4888/1965 Sherk et al 260672 3,213,150 10/1965 Cabbage 260672 DELBERT E.GANTZ, Primary Examiner.

C. R. DAVIS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,288,876 November 29, 1966 James D. Hammond et al.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

In the heading to the printed specification, line 5, for

"Mobile Corporation" read Mobil Oil Corporation column lines 23 and 24,for "dalkylation" read dealkylation column 4, line 73, for "liquidgases" read liquid and gases Signed and sealed this 19th day ofSeptember 1967.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner ofPatents

1. A PROCESS FOR THE DEALKYLATION OF AN ALKYLAROMATIC HYDROCARBON WHICHCOMPRISES INDIRECTLY PREHEATING A CHARGE COMPRISING HYDROGEN AND ANORMALLY LIQUID ALKYLAROMATIC HYDROCARBON FEED STOCK IN A RATIO OF ATLEAST 4000 S.C.F. OF HYDROGEN PER BARREL OF SAID FEED STOCK IN APREHEATING ZONE WHEREIN THE MAXIMUM TEMPERATURE OF HEAT TRANSFERSURFACES IN CONTACT WITH SAID CHARGE IS MAINTAINED AT NOT MORE THANABOUT 65*F. ABOVE THE TEMPERATURE OF THE PROXIMATE PORTION OF THECHARGE, INTRODUCING SAID PREHEATED CHARGE AT A TEMPERATURE BETWEEN ABOUT1100